Cellular telephone system and method for dynamically switching between call routing options

ABSTRACT

Disclosed is a system and method for enabling a cellular telephone subscriber located in a foreign service area to designate how calls placed to the subscriber should be handled by entering selections (such as call forwarding, caller notification) from the keyboard of his mobile telephone set. When these selections are received by a foreign service MTSO, the foreign service MTSO validates the roaming subscriber and the services that are available to the subscriber and then notifies the home MTSO how calls received at the home site should be handled. If the caller is to receive calls in the foreign service area (either forwarded calls or direct calls to the foreign service area), the foreign MTSO assigns a temporary roaming number to the subscriber for use in the foreign service area after the subscriber has been validated.

BACKGROUND OF THE INVENTION

The present invention relates to cellular telephone communicationsystems, and more particularly to a system and method that provides fordynamic switching between call handling options such as callernotification and forwarding.

A conventional cellular system consists of a Mobile Telephone SwitchingOffice (MTSO) which is surrounded by a set of cell sites. A mobilesubscriber establishes a radio frequency (RF) communications link with acell site by initiating a call. Each of the cell sites is coupled to theMTSO. The MTSO is also coupled to the Public Switched Telephone Network(PSTN), by dedicated lines. The range of a particular cellular serviceis determined by the geographic location of cell sites. When asubscriber to a cellular mobile telephone service leaves the range thatis covered by his home service area and enters a foreign service area,calls that are received need to be handled in an appropriate manner. Forexample, the caller could be informed of the location of the subscriber;the calls could be forwarded directly to the subscriber; or the callscould be routed through the subscriber's voice mail service.

The forwarding of calls directly to the subscriber is not alwaysappropriate, because in the present cellular telephone environment, thesubscriber pays for the cost of the call. This means that a subscribermay be receiving calls that he does not want to receive and that he hasto pay for. For this reason, subscribers frequently have calls sent to avoice mailbox or have the caller place the call directly to a foreignservice area, in which case the caller would pay the long distancetelephone charges. A subscriber using a cellular telephone in a foreignservice area is generally referred to as a "roamer".

In order for a subscriber to instruct a caller to call a roamingsubscriber, the subscriber would have to manually inform each potentialcaller of the roamer access number of the cellular telephone system thatthe roamer is using. Since the roamer could be moving from one roamersite to another, this is not always practical. Call delivery systemsprovided by some switch manufacturers (such as Motorola, AT&T andEricsson) as well as the Follow Me Roaming product offered by GTE reducethis inconvenience to some extent but do not provide options of thepresent invention.

It is therefore a principal object of the present invention to provide acellular telephone system and method that dynamically switches betweencall handling options.

Another object of the present invention is to provide a cellulartelephone system and method that automatically initiates call forwardingto a foreign service area after a subscriber places a first call in theforeign service area or enters a foreign service area with the cellularphone switched on.

SUMMARY OF THE INVENTION

Accordingly, in the present invention, a subscriber in a foreign servicearea site is able to designate how his call should be handled byentering selections (such as call forwarding, caller notification) fromthe keyboard of his mobile telephone set. When these selections arereceived by a foreign service MTSO, the foreign service MTSO sends arequest to the central host computer which validates the roamingsubscriber and the services that are available to the subscriber andthen notifies the home MTSO how calls received at the home site shouldbe handled. If the caller is to receive calls in the foreign servicearea (either forwarded calls or direct calls to the foreign servicearea), the foreign MTSO assigns a temporary roaming number to thesubscriber for use in the foreign service area after the subscriber hasbeen validated.

These and other features and objects of the present invention will bemore fully understood from the following detailed description whichshould be read in connection with several drawings in whichcorresponding reference numerals refer to corresponding parts throughoutthe several views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the cellular telephone system of thepresent invention which provides for dynamic switching between callrouting options;

FIG. 2 is a diagram of the functions performed by the elements of thecellular telephone system shown in FIG. 1 when the subscriber selects,the call forwarding option;

FIG. 3 is a diagram of the functions performed by the elements of thecellular telephone system shown in FIG. 1 when the subscriberdeactivates the selected call routing option.

FIG. 4 is a diagram of the functions performed by the elements of thecellular telephone system shown in FIG. 1 when the subscriber selectsthe caller notification option;

FIG. 5 is a diagram of the functions performed by the elements of thecellular telephone system shown in FIG. 1 when automatic call forwardingis put in effect;

FIG. 5a is a diagram similar to FIG. 5 except that the system uses anautonomous registration system;

FIG. 6 is a schematic diagram of the elements of the voice responsesystem of the cellular telephone system shown in FIG. 1;

FIG. 7 is a flow chart of the operation of the cellular telephone systemshown in FIG. 1;

FIG. 8 and 9 are flow charts of the overall control of the cellulartelephone system shown in FIG. 1 which allows that system to provide forthe dynamic switching of call routing options.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, each MTSO has a voice response system (VRS) 12 andan interface that connects to a central host computer 14. In order tosimplify the following discussion, only two MTSO sites are shown, but anactual implementation would have multiple MTSO sites, similarlyconfigured, and connected to a central host computer. In addition, whileone of the MTSO sites is designated as a home site, and the other isdesignated as a roam site, either site will function as either a home ora roam site.

The VRS 12 is connected to the MTSO switch 16 via a digital telephoneinterface 18. The home MTSO switch 16 is programmed to route all callsfor a roamer that has selected a call routing option. In a preferredembodiment a roamer selects a call routing option by entering specificcodes in his handset, either in his home service area or a foreignservice area. The following sequences are one set that may be used toselect a variety of sequences:

    ______________________________________                                               Call Routing Function Being Requested Under                            Code   Dialed Code                                                            ______________________________________                                        *31    Activates transparent call forwarding                                  *32    Activates caller notification                                          *30    Deactivates roaming service                                             *310  Deactivates transparent call forwarding/(route                                to voice mail)                                                          *320  Deactivates caller notification/(route to voice mail)                  ______________________________________                                    

Referring now to FIG. 2, the activating of transparent call forwardingwill now be described. When a roamer dials *31, the foreign MTSO switch16 sends the mobile identification number (MIN) and the code for theselected call routing option to the VRS 12. In a preferred embodimentthe physical interface is a T-1 (DSl span), and multi-frequency (MF)signalling is utilized to pass the information from the switch 16 to theVRS 12. The VRS 12 accepts the information and communicates it to thecentral host computer 14 via a data communications link 17.

A central host computer 14 after receiving the mobile identificationnumber and selection code for the call routing option validates thesubscriber to assure, among other things, that the subscriber's carrierin his home service area is part of the network companies supportingcall forwarding. The appropriate commands are then sent by the centralhost computer 14 to the home MTSO to set up the call routing option thathas been specified by the roamer. If the call routing option that wasselected by the roamer is transparent call forwarding, the central hostcomputer 14 obtains a temporary telephone number from the roam MTSO thatwould be associated with the MIN of the roamer. This temporary telephonenumber must be assessable via the PSTN because it is the phone number towhich the caller will be transferred. After the temporary telephonenumber is obtained from the roam MTSO, the central host computer 14signals the home MTSO to complete activation. The central host computer14 first determines that the roamer is currently call forwarded orno-answer transferred to other numbers, and if so, these numbers aresaved and the existing feature is deactivated so that calls will nolonger be directed to the numbers where they were previously directed.If the roamer does not have the no-answer feature, the feature istemporarily provided. The no-answer transfer telephone number that isentered is the temporary number that was obtained previously from theroam MTSO.

Referring now to FIG. 3, when the central host computer 14 determinesthat it is time to deactivate a call routing of a roamer, it sendscommands simultaneously to a home MTSO and the roam MTSO. At the homeMTSO the roamer is restored to his original call routing status with theformer call forwarding and no-answer transfer numbers restored. At theroam MTSO, the temporary phone number that has been obtained is freed sothat is can be used for other roamers. Deactivation is initiated byeither the roamer selecting a deactivation of the call forwarding fromthe mobile telephone by dialing *310, or automatically after x number ofhours (where x can be set dynamically by the carrier).

Referring now to FIG. 4, if the roamer selects the call routing optionof caller notification by dialing *32, all calls to the roamer will berouted to the VRS 12 located at the home site. The central host computer14 will check with the home MTSO to determine if the roamer is currentlycall-forwarded or no-answer transferred to other numbers, and if so,these numbers are saved and the existing feature is deactivated. If theroamer does not have the no-answer feature, the feature is temporarilyprovided by providing a no-answer telephone number to the home switch.The no-answer transfer telephone number that is entered is the numberthat connects to the VRS 12 at the home MTSO site. The central hostcomputer 14 also provides to the home switch a switch code of the roamsite where the roamer is located. The home switch is programmed to outpulse this switch code as an MF digit spill at the start of the call tothe VRS. The VRS is programmed to analyze this digit spill and play amessage to the caller which indicates where the roamer is located, andthe roamer port access number that should be used to call the roamer. Anexample of a message that would be played is: "The person that you havecalled is out of the local area. If you wish to reach this person,please call 609-226-7626 in Atlantic City, New Jersey."

A different message for each possible roam site is required. The VRS 12maintains a table of switch codes and roam site messages. Preferably,each roam site message includes a roamer port access number and the nameof the city where the roam MTSO is located.

If a roaming subscriber does not select a specific option when he isroaming, the system of the present invention will automatically activatea subscriber for automatic call forwarding when the roamer makes hisfirst call in the roam site. In FIG. 5, the information flow for thisactivation of automatic call forwarding is shown. When the roamer makeshis first call, the roam switch sends the MIN, roamer's electronicserial number (ESN) and the system ID (SID) of the roam switch to thecentral host computer 14. The central host computer 14 obtains thetemporary phone number from the roam switch and sets up the roamer withcall forwarding the temporary phone number to the home switch. Thecentral host computer saves existing call handling settings.

A preferred embodiment of the elements of the VRS 12 are shown in FIG.6. The VRS processor 30 in a preferred embodiment is implemented with aHewlett-Packard Vectra ES/12 personal computer, available fromHewlett-Packard Corporation. The VRS processor 30 is equipped with2Mbytes of Random Access Memory (RAM), a 40Mbyte hard disk drive, and adata communications port. The telephonic/voice interface 32 includesboards from Dialogic Corporation, such as a DTI124 T-1 Interface board,4 port MF/40 boards and 4 port D40/B Voice Communications boards. Asingle VRS can be expanded to handle 24 simultaneous telephone calls byadding in the appropriate quantity of MF/40 and D40/B boards. The datacommunications interface is an asynchronous, 1200 baud link, utilizingXON/XOFF protocol. The processor is coupled to the MTSO via theTelephonics/Voice interface 32. The physical interface is a T-1interface and Multi-Frequency (MF) is utilized for signalling. Thechoice of T-1 and MF was based primarily on the interfaces that are mostreadily and economically available at the MTSO. Other schemes, such asanalog transmission and DTMF signalling could just as readily have beenutilized. A data communications interface 17 couples the VRS processor30 to the central host computer, and a display console is provided foroperator use.

FIG. 7 shows the steps that occur when the VRS establishes the callhandling setup and processes calls to the roamer. For the roamer toestablish the desired call routing option desired, the roamer dials theselection from the pushbutton keypad of his mobile telephone handset instep 40. In step 42, the MTSO, in turn, routes the selection that theroamer made and the MIN of the roamer to the VRS 12. The VRS determineswhether the call is from a roamer setting up his call handling or a callto a roamer, by counting in step 44 the number of digits that were sent.The roam switch ID code is six digits. The selection code plus the MINof the roamer is always in excess of six digits. In step 44, the VRS 12determines if the number of digits is greater than six, and if it is, instep 46 the roamer selection, MIN of the roamer and the roam switch IDcode are sent to the central host computer 14. The VRS 12 keeps recordsof the total number of calls that were made and the selections that weremade by the roamer, as shown in step 48. This information is availableto the system user as a report. These reports can be obtained eitherautomatically (at a predetermined time each day) or on the demand of theuser. Monthly usage statistics reports are also provided. If the numberof digits that was received was six, the VRS 12 searches a directory ofswitch codes. Corresponding to each switch code is a unique audiomessage which identifies the switch by location and roamer accesstelephone number and this message is fetched in step 50. The audiomessage that is associated with the particular roam site is then playedto the caller in step 52. The VRS 12 keeps track of the total number ofcalls as well as the number of calls that are made to roamers at eachroam site in step 54.

In a preferred embodiment, the central host computer 14 is a VAXcomputer sold by Digital Equipment Corporation and is controlled by thefollowing six distinct software modules that control the functionsinvolved in delivering cellular phone services to subscribers.

    NCDS.sub.-- DISPATCH

    NCDS.sub.-- CONTROL

    NCDS.sub.-- RETRY

    NCDS.sub.-- PURGE

    NCDS.sub.-- VALIDATE

    NCDS.sub.-- ALARM

Referring to FIG. 8, the operation of the central host computer 14 ascontrolled by NCDS will now be described.

The purpose of the NCDS₋₋ DISPATCH module is to determine if thesubscriber's request is valid, decide how to process the request, andthen obtain the information that is needed to process the request. Asillustrated in step 60, the central host computer 14 accesses the RoamerAgreement Database to determine if the service that is being requestedby the Roamer is consistent with the agreement that exists between thehome and roam carriers and the level of service that the roamer hasselected. If the request is determined to be a valid request, thecentral host computer 14 accesses a Positive Roamer Verification (PRV)Database to obtain the routing and switch information as shown in step62. After this operation has been completed, the central host computercomes under the control of the NCDS₋₋ CONTROL module.

NCDS₋₋ CONTROL takes the requests that are received by the central hostcomputer 14 and sends out the commands to the switches. Some of the moreimportant commands that are sent out by the central host computer whileoperating under NCDS₋₋ CONTROL are:

    FEATURES.sub.-- INQUIRY

    ENABLE.sub.-- NOTIFICATION

    DISABLE.sub.-- NOTIFICATION

    ALLOCATE.sub.-- TDN

    DEALLOCATE.sub.-- TDN

    ENABLE.sub.-- TRANSFER

    DISABLE.sub.-- TRANSFER

    NCDS.sub.-- RETRY

    NCDS.sub.-- PURGE

    NCDS.sub.-- VALIDATE

    NCDS.sub.-- ALARM

The NCDS₋₋ RETRY command is enabled if the command-receiving switch isunable to successfully complete a requested or required option, whichwould occur, for example, if one of the MTSOs was disabled. As shown instep 66, this process is repeated periodically until it is successful.

In step 68, when a FEATURES₋₋ INQUIRY command is issued, the centralhost computer accesses the home switch and returns the Electronic SerialNumber (ESN) of the roamer and a snapshot of the current call forwardingconfiguration for that subscriber. The ESN is used to verify that thesubscriber is valid. The call forwarding configuration is used todetermine how to activate the subscriber, and how to restore asubscriber's original settings. The central host computer thendetermines, in step 70, if the roamer selection was for callernotification service or for transparent call forwarding service. If theselection was for caller notification, the central host computer issuesan ENABLE₋₋ NOTIFICATION command which accesses the home switch and setsthe subscriber's call forwarding features to caller notification asillustrated in step 72.

If the roamer selects call forwarding, the central host computer issuesa ALLOCATE₋₋ TDN command to obtain a temporary telephone number from theroam switch. As shown in step 74, the central host computer accesses the"roam" switch and obtains a temporary number for the roamer to use. Thecentral host computer then issues an ENABLE₋₋ TRANSFER command to setthe subscriber's call forwarding to the temporary telephone number thatwas previously obtained from the roam switch. As shown in step 76,ENABLE₋₋ TRANSFER causes the central host computer to access the "home"switch and change the roamer's call transfer number to the temporarynumber.

With reference to FIG. 9, the commands issued by the central hostcomputer 14 to deactivate the call handling setup that had beenestablished for a roamer to return the roamer to his original state willnow be described. In step 82, the central host computer 14 operatingunder control of the NCDS₋₋ CONTROL module determines if the roamerselection was for caller notification service or for transparent callforwarding service. If the roamer selection was caller notification, theDISABLE₋₋ NOTIFICATION command is issued to access the home switch andreturn the subscriber's call forwarding features to their originalsettings as shown in step 84. If the roamer selection was transparentcall forwarding, the DEALLOCATE₋₋ TDN function is utilized in step 86 toreturn the temporary telephone number to the roam switch when the roameris through using it. Then in step 88, the DISABLE₋₋ TRANSFER functionreturns the subscriber's call forwarding settings to their originalsettings.

In order to keep the central host computer records to a manageablelevel, a NCDS₋₋ PURGE function is enabled once each hour to issue adeactivate request for every subscriber that has expired since the lastpass. The expiration criteria is that service is deactivated 24 hoursafter the last call has been made by the roamer in the roam market.

The NCDS₋₋ VALIDATE command is issued to periodically revalidate anysubscribers that are still active and have not been validated by NCDS inat least 24 hours by sending a FEATURES₋₋ INQUIRY command to the homeMTSO. If the subscriber is now invalid, a DEACTIVATE request is issued.Finally, as a safety system, the NCDS₋₋ ALARM function periodicallyscans the list of all registered subscribers (regardless of theircurrent call handling activation status) and reports any abnormalities.

In a preferred embodiment shown in FIG. 5a, the system also includes anautonomous registration system which enables an MTSO to detect thepresence of a cellular phone in its home service area simply by virtueof the phone being switched on in the geographic area served by the MTSOor by virtue of a phone that it is on as the subscriber moves into thegeographic area served by the foreign service area MTSO. In other words,the MTSO is capable of detecting the presence of a cellular phonesubscriber in a service area even before the subscriber makes a call.This enables the subscriber to request that a system treat aregistration event as an implicit selection of a call handling option.To do this, when a subscriber drives into a new foreign service areawith the cellular phone powered-up, the cellular phone automaticallydetects a change in system ID and sends a registration message to theforeign service area MTSO identifying itself. This feature is built intoalmost all existing cellular phones. The foreign service area MTSOreceives the registration message and notifies a central host computerthat a subscriber has been registered. The central host computer checksto see if the caller has indicated that he wanted to activate a certaincall handling option when he is in that particular foreign service area,and if that is the case, that service is then activated.

While the foregoing invention has been described with reference to itspreferred embodiments, various alterations and modifications will occurto those skilled in the art. All such alterations and modifications areintended to fall within the scope of the appended claims.

What is claimed is:
 1. A method for enabling a cellular telephonesubscriber to dynamically specify the manner in which calls to thesubscriber are to be handled when the subscriber is located in a foreignservice area, the method comprising:receiving at a roam site MTSOinformation indicating which of at least two call handling options isbeing requested by the subscriber; validating the subscriber requestingthe call handling option; providing information to a subscriber's homeservice area MTSO that indicates, based on one of said at least two callhandling options, how calls to the subscriber are to be handled whilethe subscriber is located in the foreign service area; saving callhandling settings that existed prior to the time subscriber specified amanner in which the subscriber's calls are to be handled in order toenable the subscriber to restore previous call handling settings.
 2. Asystem for enabling a cellular telephone subscriber to dynamicallyspecify the manner in which calls to the subscriber are to be handledwhen the subscriber is located in a foreign service area, the systemcomprising:means for receiving one of at least two call handlinginstructions from a subscriber in a foreign service area and forproviding from the foreign service area a mobile identification number,and a code representing the call handling instructions issued by thesubscriber; a central host processor means for validating the subscriberissuing call handling instructions and for providing information to thesubscriber's home service area concerning which of said at least twocall handling instructions are to be implemented while the subscriber islocated in the foreign service area; means for saving call handlinginstructions that existed prior to a selection of a call handling optionby the subscriber in order to enable the subscriber to restore previouscall handling settings.